Electrostatic film capacitors with high volumetric energy density, high operating temperature, and long lifetime are important components for pulse-power, automotive, and industrial electronics. Generally, capacitors are energy-storing devices having two parallel conductive plates separated by a thin layer of an insulating (dielectric) film. When a voltage is applied across the plates, the electric field in the dielectric displaces electric charges, and thus stores energy. The amount of energy stored by a capacitor depends on the dielectric constant of the insulating material, the applied voltage, and the dimensions (total area and thickness) of the film. Consequently, in order to maximize the total amount of energy that a capacitor can accumulate, a dielectric constant and breakdown voltage of the film needs to be maximized, and a thickness of the film minimized. The physical characteristics of the dielectric material in a capacitor are the primary determining factors for the performance of the capacitor, so improvements in one or more of the physical properties of the dielectric material of a capacitor can result in corresponding performance improvements in the capacitor component, usually resulting in performance and lifetime enhancements of the electronics system or product in which the capacitor is embedded.
Electrostatic film capacitors made from biaxially-oriented poly(propylene) (BOPP) have been used in applications requiring a low dissipation factor, high insulation resistance and low dielectric absorption, such as in electrical appliances, electronic equipment, oven and furnaces, refrigerators, automobiles, and home appliances. The low dielectric constant (Dk) of BOPP, which is about 2.2, and its maximum service temperature of about 100° C. limits the use of BOPP capacitors in applications requiring high operating temperatures and/or high energy densities. Other thermoplastic materials, such as polyethylene terephthalate (PET), polyethylene naphthalate (PEN) and polycarbonate (PC) with Dk>3.0 could be reasonable alternatives; however, capacitors made from these films can only be used at operating temperatures as high as about 125° C., therefore not meeting a desired high temperature performance capability. Several materials which meet high temperature capabilities, such as polyphenylene sulfide (PPS) and polyether ether ketone (PEEK), are limited by an instability of electrical properties at temperatures exceeding 150° C., thus making them less desirable for use in capacitors. Thus, there is an ongoing need to develop and/or improve dielectric materials for use in capacitors.